A novel analytical protocol for the determination of free fatty acids (FFAs; saturated, monounsaturated and polyunsaturated) in shellfish using electrospray ionisation and liquid chromatography–mass spectrometry (LC–MS) is described. Total lipids were extracted from four commercially important shellfish species using chloroform-methanol in a modification of the traditionally used Bligh and Dyer method. FFAs were recovered from lipidic shellfish extracts by solid-phase extraction (SPE) on an aminopropyl-silica column using a 98:2 v/v diethyl ether (DEE)-acetic acid solution. Ether extracts containing the FFAs were evaporated and reconstituted in 70:30 v/v methanol–chloroform before analysis by LC–MS. The limits of quantification (LOQs) of the method ranged from 60 to 560 ?g g?1 wet weight depending on the different FFAs determined with selected ion monitoring (SIM). Results demonstrate that LC–MS is well suited for identification and quantification of FFAs in shellfish and negates the use of sample derivatisation required in gas chromatographic analysis.